If you have worked with PowerShell remoting then you will have seen this error before:
: Connecting to remote server BLAH failed with the following error message : The WinRM client received an HTTP status code of 403 from the remote WS-Management service. For more information...
It is not a happy message, especially when you have been using PowerShell to remotely manage the particular server for ages! So then you try remoting from another client and it works! You go back to your original client and try remoting to anything else and it fails...dohh! "But this worked just yesturday!" you scream.
Ahh, little things can make a big difference and in my case the issue was related to a VSTS Agent update that I did the day before. In order for the new version of the agent to communicate with VSTS in the cloud I needed to set a WinHTTP proxy. Once the agent was configured I could use a .proxy file in the agent directory instead...but I forgot to remove the WinHTTP proxy and in so doing broke PS Remoting.
Here is the story in a nutshell:
Without a proxy I can enter a remote PS session but with one I can not and I get the error, which sucks if you forgot that you had set the proxy. Best to remember that WinRM uses the HTTP protocol so proxy settings matter.